Radiocarbon dating can be used to directly date
Later inter-laboratory measurements put the ratio at 1.5081 (Currie and Polach, 1980).
Aon is the activity in counts per minute of the modern standard, Asn is the equivalent cpm for the sample. A CRA embraces the following recommended conventions: correction for sample isotopic fractionation (delta C13) to a normalized or base value of -25.0 per mille relative to the ratio of C12/C13 in the carbonate standard VPDB (more on fractionation and delta C13); Three further terms are sometimes given with reported radiocarbon dates. All are expressed in per mille notation rather than per cent notation (%).
It is vital for a radiocarbon laboratory to know the contribution to routine sample activity of non-sample radioactivity.
Obviously, this activity is additional and must be removed from calculations.
A time-independent level of C14 activity for the past is assumed in the measurement of a CRA.
The activity of this hypothetical level of C14 activity is equal to the activity of the absolute international radiocarbon standard.
Standard errors released with each radiocarbon assay (see below) are usually rounded by convention (Stuiver and Polach, 1977).